In many parts of the United States, rainfall is insufficient and/or too irregular to keep turf and landscaping green and therefore irrigation systems are installed. Such systems typically include a plurality of underground pipes connected to sprinklers and valves, the latter being controlled by an electronic irrigation controller. One of the most popular types of sprinklers is a pop-up rotor-type sprinkler. In this type of sprinkler a tubular riser is normally retracted into an outer cylindrical case by a coil spring. The case is buried in the ground and when pressurized water is fed to the sprinkler the riser extends. A turbine and a gear train reduction are mounted in the riser for rotating a nozzle turret at the top of the riser. The gear train reduction is often encased in its own housing and is often referred to as a gear box. A reversing mechanism is also normally mounted in the riser along with an arc adjustment mechanism.
The gear box of a rotor-type sprinkler can include a series of staggered gears and shafts wherein a small gear on the top of the turbine shaft drives a large gear on the lower end of an adjacent second shaft. Another small gear on the top of the second shaft drives a large gear on the lower end of a third shaft, and so on. Alternately, the gear box can comprise a planetary arrangement in which a central shaft carries a sun gear that simultaneously drives several planetary gears on rotating circular partitions or stages that transmit reduced speed rotary motion to a succession of similar rotating stages. It is common for the planetary gears of the stages to engage corresponding ring gears formed on the inner surface of the gear box housing. See, for example, U.S. Pat. No. 5,662,545 granted to Zimmerman et al. A planetary gear box is desirable from the standpoint of being more compact, yet more robust, than a staggered gear box.
Two basic types of reversing mechanisms have been employed in commercial rotor-type sprinklers. In one design a reversing stator switches water jets that alternately drive the turbine from opposite sides to reverse the rotation of the turbine and the gear box. See for example, U.S. Pat. No. 4,625,914 granted to Sexton et al. The reversing stator design typically employs a long metal shaft that can twist relative to components rigidly mounted on the shaft and undesirably change the reverse point. Users setting the arc of sprinklers that employ a reversing stator design do not get a tactile feel for a stop at the set reverse points. Turbines in reversing stator designs usually do not produce much power.
A more popular design for the reversing mechanism of a rotor-type sprinkler includes four pinion gears meshed together and mounted between arc-shaped upper and lower frames that rock back and forth with the aid of Omega-shaped over-center springs. One of the inner pinion gears is driven by the gear box and the pinion gears on opposite ends of the frames alternately engage a bull gear assembly. See for example, U.S. Pat. Nos. 3,107,056; 4,568,024; 4,624,412; 4,718,605; and 4,948,052, all granted to Edwin J. Hunter, the founder of Hunter Industries, Inc., the assignee of the subject application. The entire disclosures of said patents are hereby incorporated by reference. While the reversing frame design has been enormously successful, it is not without its own shortcomings. It involves a complicated assembly with many parts and can have operational failures. The main drawback of the reversing frame design is that the pinion gears are relatively weak compared to the gears in the gear box. Therefore, it is not uncommon for the pinion gears to break, wear out, or become stripped during operation of this kind of rotor-type sprinkler.
Non-revering, full circle rotation sprinklers such as golf rotors and stream sprinklers have been commercialized that have incorporated planetary gear boxes. Rotor-type sprinklers have also been commercialized that have combined planetary gear boxes and reversing mechanisms, however, in all such sprinklers all parts of the reversing mechanisms have been external to the gear box. See for example, U.S. Pat. No. 4,892,252 granted to Bruniga.